The 6 Most Common Mistakes in Specifying ERVs (and How to Avoid Them)

The Challenge:

In an effort to ensure adequate ventilation, engineers sometimes size ERVs based on worst-case scenarios. The intent is solid, but without diversity factors or modulation, this can lead to oversizing, higher energy use, and more noise than necessary. On the flip side, under sizing can lead to occupant discomfort or code compliance issues.

Contributing factors: 

• Applying full occupancy ventilation to every space simultaneously 

• Not accounting for internal gains or infiltration variability 

• Using default airflow values without project-specific modeling 

Engineering experts agree: 

Use ASHRAE 62.2 or 62.1 as a starting point, but refine sizing based on realistic occupancy and usage profiles. Diversity factors are especially helpful in multi-family buildings, where not every unit requires full ventilation simultaneously. Some systems on the market offer variable-speed operation to better match partial loads. Even without full modulation, proper sizing and smart control strategies can significantly reduce energy use and improve comfort. 

The Challenge:

A well-performing ERV in one region may fall short in another. Local climate and seasonal extremes impact how the unit performs and whether frost buildup or humidity transfer could be a concern. 

Common oversights: 

• Using a single ERV model across different project geographies 

• Not specifying frost protection or bypass capability in colder climates 

• Assuming sensible-only recovery works everywhere 

Engineering experts agree: 

Use tools like the DOE Building America Solution Center or climate zone maps to guide product selection. Pay close attention to core type (enthalpic vs. sensible), defrost strategy, and the value of latent energy recovery.  

The Challenge:

Even a properly sized ERV can underperform if the control strategy isn’t clearly defined. In the field, ERVs are sometimes set to run continuously, regardless of occupancy or air quality, leading to unnecessary energy use, noise concerns, or early wear.

Why it happens: 

• Control strategy isn’t outlined in the spec 

• Decisions about controls are left to the installer 

• The selected ERV doesn’t match the control expectations 

How to avoid it: 

Controls should be part of the design conversation, not an afterthought. Specify how the system should operate: continuous, intermittent, boost mode (e.g., tied to a bathroom switch or range hood), or demand-based using timers or TVOC-sensing controls. Simpler is often better, especially in residential and multi-family settings. Select systems with factory-installed control options when possible and provide clear wiring diagrams to support a consistent setup. 

The Challenge:

ERVs placed in attics, closets, or tight corners can be difficult to access, hard to duct efficiently, and vulnerable to environmental stress. 

Why it happens: 

• Architectural constraints limit mechanical room space 

• Aesthetics take priority over duct routing 

• Coordination between disciplines comes late 

Engineering experts agree: 
Prioritize service access and airflow performance when selecting placement. ERVs should ideally be located in conditioned or semi-conditioned spaces with enough clearance for maintenance. Use BIM objects to catch placement conflicts early. 

Include manufacturer-recommended clearance requirements directly in your spec. Highlight access panels in your Revit model. Where possible, recommend hinged panels or bottom-access configurations for tight areas. 

The Challenge:

Even a properly sized ERV will not perform as intended if  if the duct system introduces too much static pressure or allows air to bypass. 

Why it’s tricky in multi-family: 

• Shared ducting increases the risk of odor transfer 

• Excessive bends and transitions raise static pressure 

• Return air and exhaust paths are sometimes mismatched 

Engineering experts agree: 

Design with low-resistance duct runs and balance points for commissioning. Avoid shared exhaust ducts between units unless a common shaft is properly sealed and balanced. Include test ports and dampers to allow field verification. 

Include commissioning as a deliverable: airflow balancing, control verification, and occupant system training. Reference manufacturer guidelines for testing and adjusting the unit. A small investment at the start pays off in performance and peace of mind. 

The Challenge:

When specs are vague or copied from previous jobs, they’re more likely to be value-engineered, misinterpreted, or delayed in review. 

How it happens: 

• Tight timelines lead to copy-paste details 

• Accessories, control types, or interface requirements are left out 

Engineering experts agree: 

Develop a comprehensive spec package that includes: 

• Model numbers and airflow capacities 

• Control protocol compatibility 

• Required accessories and access notes 

• Installation or balancing instructions